One of the defining features of addictive behavior is its persistence despite potentially severe adverse outcomes. To further understand why addicts fail to learn from negative outcomes, we propose to explore the role of a newly identified brain region, the rostromedial tegmental nucleus (RMTg), which we and others have recently shown to encode negative reward prediction errors, and to be critically involved in a variety of aversive behaviors. We hypothesize that impairment of this structure leads to an addiction phenotype in which animals persistently seek outcomes despite aversive outcomes. We propose two aims, the first of which is designed to better understand the basic mechanisms by which the RMTg contributes to learning about negative outcomes. Our second aim is more translational, exploring the role of the RMTg in cocaine-seeking under punishment, as well as its contribution to individual variation in propensity to develop addictive behaviors.